Characteristics of flash boiling and its effects on spray behavior in gasoline direct injection injectors: A review

The flash boiling phenomenon occurs when the ambient pressure around fuel is lower than the saturation pressure. This is followed by the formation and growth of bubbles. Flash boiling has been regarded as a promising method to improve the atomization of fuel sprays and to reduce emissions without a high-pressure injection system, which has recently become a popular topic. Therefore, it is necessary to summarize the current research status of flash boiling sprays. This review seeks to provide on overall understanding of flash boiling sprays in gasoline direct injection (GDI) injectors and includes theoretical, experimental, and numerical studies relevant to the flash boiling process. The effects of the degree of superheating and injector configuration, which includes the spacing angle, nozzle number and nozzle length, on spray behavior under flash boiling conditions are analyzed. Furthermore, in order to gain a deep understanding of the collapse mechanism of the spray, the formation of the collapse is explained from several aspects, including the velocity field, temperature field, vapor concentration field, and droplet diameter. A thorough understanding of flash boiling spray behaviors and the collapse mechanisms can help further technological applications, such as injector design and injection strategies. Finally, an overview of the available theoretical models and their applications is presented, which provides a simple and concise method of understanding flash boiling spray behavior.